Mitt Romney’s Illinois win could be the beginning of the end of the Republican nomination fight. In order to get there, he faces two challenges: He’ll have to convince on-the-sidelines Republicans to endorse his candidacy, contribute to his campaign, and muscle Rick Santorum and Newt Gingrich out of the race. And he’ll also have to persuade the media to reflect the reality that Romney is the only candidate who can win a majority of the delegates needed for the nomination and that he has a good chance of reaching that milestone well before the party meets for its Tampa convention in late summer.

The Romney campaign had made progress on both those fronts before his Illinois win, but the commanding victory is likely to accelerate his cause in the coming days. Once that happens, the normal rules that have prevailed in past nomination fights will kick back in. Santorum and Gingrich can choose to stay in the race, but they will be marginalized and unable to slow Romney down in his accumulation of delegates. They will become ghost candidates, on the ballot and campaigning, but effectively lifeless. Chatter about a contested convention will be greatly diminished.

Santorum probably has one more chance to change the paradigm with a win in Wisconsin on April 3, after an expected victory in Louisiana on Saturday. But even if that happens, Romney will win many more delegates in a cluster of northeastern states over the next month.

There has been much debate about whether a long nomination fight helps or hurts general election prospects, but a prolonged battle usually weakens a candidate. Barack Obama’s 2008 experience, which allowed him to learn, strengthen, and familiarize himself with the process and voters, was the exception. Romney’s tussle with Santorum and Gingrich is not building him up, and his campaign knows that.

In the last days before the Illinois vote, and in his election night victory speech, Romney refocused his rhetoric on a philosophical contrast with President Obama, virtually ignoring his GOP opponents. With Santorum’s failure to best Romney in another major industrial state, it may well be that the Republican frontrunner can now focus on his rival in the White House all the way through November.